Gridview下的DropDownList有关问题,很郁闷_ASP.NET

Gridview下的DropDownList问题,很郁闷.
GridView中的第条数据行都绑定了一个DropDownList,要取得DropDownList所在行的SelectedValue和DataKeys的值.
本来已经实现了.后来不记得改动了哪里又不能实现了.很郁闷.请各位指点一下.
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<asp:TemplateField>
<ItemTemplate>
<asp:DropDownList ID="ddlSubCht" runat="server" DataSourceID="objSubCht" DataTextField="SubName" DataValueField="SubId" AutoPostBack="True" OnSelectedIndexChanged="ddlSubCht_SelectedIndexChanged" >
</asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
////////////////////////////////////

C# code

 
 protected void ddlSubCht_SelectedIndexChanged(object sender, EventArgs e) 
         { 
             for (int i = 0; i  < gvCategories.Rows.Count; i++) 
             { 
                 DropDownList ddl = (DropDownList)gvCategories.Rows[i].FindControl("ddlSubCht");//问题1:在Debug下发现不能找到控件 
                 int ddlint = Convert.ToInt32(ddl.SelectedValue);//问题2:提示"未将对象引用设置到对象的实例" 
                 int key = (int)gvCategories.DataKeys[i].Value;//问题3:总是返回的同一个值.我想返回的是每行对应的DataKeys 
  
                 lbl.Text= ddlint+"_"+key+"_"+isSingle.ToString();//输出 
             } 
         }

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LZ是不是少了他的Cell【】
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方法位置不对吧
------解决方案--------------------------------------------------------
1，方法位置不对
2，确实少cell[]
你不精确到单元格是找不到控件的
------解决方案--------------------------------------------------------

C# code

protected void ddlSubCht_SelectedIndexChanged(object sender, EventArgs e){   DropDownList ddl = (DropDownList)sender;   int ddlint = Convert.ToInt32(ddl.SelectedValue);   int key = (int)gvCategories.DataKeys[(ddl.Parent as GridViewRow).RowIndex].Value;   ..}
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C# codeforeach (GridViewRow row in this.GvCaseApplyList.Rows){CheckBox chkPunish = (CheckBox)row.FindControl("chkCaseApply");id=this.GvCaseApplyList.DataKeys[row.RowIndex][1].ToString();}
------解决方案--------------------------------------------------------
 DropDownList ddl = (DropDownList)gvCategories.Rows[i].FindControl("ddlSubCht");//问题1:在Debug下发现不能找到控件
  定位不对吧....你这对应的是第几行...单元格呢?
------解决方案--------------------------------------------------------
DropDownList ddl = gvCategories.Rows[i].FindControl("ddlSubCht") as DropDownList;//

另外还要精确到cell
------解决方案--------------------------------------------------------
探讨
C# code
protected void ddlSubCht_SelectedIndexChanged(object sender, EventArgs e)
{
   DropDownList ddl = (DropDownList)sender;
   int ddlint = Convert.ToInt32(ddl.SelectedValue);
   int key = (int)gvCategories.DataKeys[(ddl.Parent as GridViewRow).RowIndex].Value;
   ..
}

------解决方案--------------------------------------------------------

DropDownList ddl = (DropDownList)gvCategories.Rows[i].FindControl("ddlSubCht");
测试了一下,可以找到控件啊,你看看是不是数据什么的出错了.
------解决方案--------------------------------------------------------